Flat materials in web form, especially paper, are wound into reels. Such reels are supplied, for example, to paper-processing machines or to printing or packaging machines. During the ongoing operation of such lines it is necessary to attach the start of a new wound reel to the end of a first reel of the flat material in web form, in a flying changeover, and to join the end and start in a suitable way, without having to stop the high-speed machines during the switchover of the rolls. This operation is also referred to as splicing.
In the paper industry this operation is performed using double-sidedly self-adhesive tapes which consist essentially of a carrier layer and two layers of self-adhesive composition, in order to produce a join between the end of the old material web and the start of the new material web. In this operation, the end of the old material web becomes adhered to the start of the new material web.
In order to minimize the impulsiveness of the splicing of the radially outer end of the new roll (its start, so to speak) to, for instance, the end of the outgoing roll, when joining the old to the new web, it is necessary, in a conventional way, to accelerate the new roll to a rotational speed which is such that its peripheral speed corresponds to the speed of the old web. During this acceleration, the radially outer end is exposed to centrifugal forces, while at the same time the slip stream engages beneath the web end. So that the paper roll withstands these forces and does not “explode”, the adhesive tape used must ensure a considerable locking strength until the splice has been made. After the desired flying splice has come about, however, the desire is for an extremely low locking strength.
As a solution to this problem, DE 10 2005 051 181 A1 proposes an adhesive splicing tape comprising a splittable adhesive tape having a left-hand (l) and a right-hand (r) bounding edge, at least one of these two edges (l, r) being nonrectilinear, and the nonrectilinear edge (l) having projections (V) which are rounded at their furthest projecting points (v). Whereas nonrectilinear geometries in the splittable system ensure a balanced compromise between high locking strength in relation to the active centrifugal forces, and easy opening after the splicing operation, such adhesive tapes are associated with problems, which occur particularly when preparing wound rolls of materials in web form for splicing. For instance, in the case of nonrectilinear geometries in the splittable system, the unwinding of the adhesive tape is accompanied by stresses on the leading edges of the splitting system, which are transverse relative to the unwind direction, and also, in certain cases, by the incipient splitting of the splittable strip. Premature, incipient splitting occurs especially in the case of wave shapes or with those geometries which are characterized by a high geometric slope. To solve this problem, DE 10 2008 059 385 A1 proposes a release system having characteristic curve sections.
A further problem, however, is associated with all nonlinear geometries—wave-shaped geometries, for example—of the splittable system. Thus the preparing of a new roll of a wound material in web form involves not only the application of corresponding adhesive splicing tapes to the reels, but also the removal of release media used (“liners”) before the actual splicing operation. The forces which occur during removal of the liner generally act radially, but in practice are generally directed in a direction counter to the centrifugal forces which occur during acceleration. As a result of the forces which act during the removal of the liner material, therefore, there are stresses in the splittable system and therefore, in certain cases, an incipient splitting of the splittable strip. Where the splitting system constitutes a coherent sheetlike structure, the unwanted incipient splitting may run over a relatively long section of the splittable system, meaning that the wound roll of web-form material can no longer be used for a smooth splicing operation.
Another problem associated with the wave-form geometries described lies in an increased tendency of such adhesive splicing tapes to form creases, in the region of the splittable elements. In addition to creasing of the adhesive splicing tape itself, therefore, there may be creasing on the part of the web-form material that is wound into rolls. In both cases, unwanted incipient splitting of the adhesive splicing tapes during the acceleration phase, owing to the centrifugal forces which are acting, is promoted. In the event that the adhesive splicing tape is adhered not parallel to the axis of a wound roll of web-form material, i.e., parallel to the roll core, but instead nonrectilinearly—askew, for example—then, after the new web has been joined to the old, the splittable connecting element with wave-form geometry initially opens only in a subregion. On account of its wave-form geometry and of the associated tendency to uncontrolled complete splitting of such connecting elements, the web may become turned over, or may lift, in the region of the front edge of the adhesive splicing tape, causing creases in the region of transition from old to new web. These creases lead to raised regions, i.e., to regions with a particular thickness. Such defects cause problems in the downstream processing operations, and may be the cause of time-consuming and hence costly interruptions to the operations. The increased tendency of the adhesive splicing tapes having connecting elements with wave-form geometry to form creases is manifested also, in particular, in the case of reels, of paperlike material, for example, which have been prepared for a splicing operation and which during their storage are exposed to atmospheric humidity. When, for example, the web-form material is paper, this paper to a certain degree absorbs atmospheric moisture, and so creases or stresses occur in the transition region from web-form material to adhesive splicing tape. These stresses are transferred to the splittable elements of the adhesive splicing tape. In the case of a wave-form geometry, there may be complete opening of the splittable element.
In other words, a nonrectilinear edge design to splittable adhesive tapes within such adhesive splicing tapes as described in DE 10 2005 051 181 A1 gives rise not only to advantages, but is instead also associated with disadvantages. These disadvantages are manifested especially when the splittable adhesive tape is formulated for a “weak” incipient splitting force, this being the maximum force required to overcome the split resistance at the leading edge, in order for the splittable system to split incipiently. This is the case, for example, with very thin papers which easily tear. In such cases, a wave-form configuration of the splittable adhesive tape has the effect of increased incipient splitting of the adhesive splicing tape while the liner is being removed in preparation for the splicing operation, and also causes unwanted creasing of the adhesive tape and/or of the web-form material.
To solve the stated problems, the present invention proposes an adhesive splicing tape as described hereinbelow.